This invention relates to airspeed measuring devices, and more particularly to an improved anemometer which is especially suitable for meterological use and for use in the navigation of sailboats.
Conventional anemometers include a rotor with long radially extending spokes, and cups attached to the spokes for catching the wind and causing the rotor to spin. The speed of the wind is proportional to the revolutions of the rotor in a given period of time, and a pickup coupled to the rotor converts the speed of the rotor to a signal proportional to airspeed.
The conventional cup-type anemometer has several disadvantages. For example, when the wind blows at an angle relative to the rotational axis of the anemometer, the anemometer output generally varies with the wind angle for any given true wind speed. Thus, when the conventional anemometer is used on a sailboat, its output tends to be non-linear in response to changes in wind speed since such change also causes the boat to heel (i.e., assume a tilted position relative to a vertical plane). On some occasions, the cup-type anemometer speeds up or slows down significantly when the wind angle changes, thereby producing large wind speed errors.
A further disadvantage is that the wind speed measurement produced by many prior art anemometers contains a dead zone region for a certain range of low air speeds. Moreover, the rotor bearings of prior art anemometers are subjected to continuous combined wind loading and loading due to the weight of the rotor itself, which limits the life of the anemometer to such an extent that replacement of a bearing is required one or more times during the desired working life of the instrument.